The present invention relates to magnetic recording, and more particularly to a method and system for providing a tunneling magnetoresistance recording junction suitable for high areal density magnetic recording.
Tunneling magnetoresistive (xe2x80x9cTMRxe2x80x9d) junctions have recently become of interest for potential use in reading recording media in a magnetoresistive (xe2x80x9cMRxe2x80x9d) head. FIG. 1A depicts diagrams of a conventional TMR sensor 10 as viewed from the side. FIG. 1A depicts the shields first and second shields 24 and 26, first and second gaps 20 and 22, leads 11 and 19, and the TMR sensor 10.
FIG. 1B depicts the conventional TMR sensor 10 as viewed from the side and from an air-bearing surface or magnetic material with which the TMR sensor 10 is being used. In addition to the TMR sensor 10, FIG. 1B depicts leads 11 and 19 and first and second gaps 20 and 22, respectively. Not depicted in FIG. 1B are conventional shields 24 and 26, which partially surround the conventional TMR sensor 10. The conventional TMR sensor 10 includes a conventional antiferromagnetic (xe2x80x9cAFMxe2x80x9d) layer 12, a conventional pinned layer 14, a conventional barrier layer 16, and a conventional free layer 18. The TMR junction for the TMR sensor 10 includes the interfaces between the conventional pinned layer 14, the conventional barrier layer 16 and the conventional free layer 18. Also depicted are portions of gaps 20 and 22 that surround a portion of the TMR sensor 10. The conventional pinned layer 14 and conventional free layer 18 are ferromagnetic. The conventional pinned layer 14 has its magnetization fixed, or pinned, in place because the conventional pinned layer 14 is magnetically coupled to the conventional AFM layer 12. The conventional antiferromagnetic layer 12 is approximately one hundred to three hundred Angstroms thick. The conventional pinned layer 14 is approximately twenty to one hundred Angstroms thick. The conventional barrier layer 16 is typically five to twenty Angstroms thick and the conventional free layer 18 is typically thirty to one hundred Angstroms thick.
The magnetization of the conventional free layer 18 of the TMR sensor 10 is biased in the plane of the page when there is no external magnetic field, but is free to rotate in response to an external magnetic field. The conventional free layer 18 is typically composed of Co, Co90Fe10, or a bilayer of Co90Fe10 and permalloy. The magnetization of the conventional pinned layer 14 is pinned perpendicular to the plane of the page. The conventional pinned layer 14 is typically composed of Co, Fe, or Ni. The conventional barrier layer 16 is typically composed of aluminum oxide (Al2O3).
For the conventional TMR sensor 10 to function, a bias current is driven between the leads 11 and 19, perpendicular to the plane of the layers 12, 14, 16 and 18 of the conventional TMR sensor 10. Thus, the TMR sensor 10 is known as a current perpendicular to the plane (xe2x80x9cCPPxe2x80x9d) junction. The direction of flow of the bias current is depicted by the arrow 24. The MR effect in the conventional TMR sensor 10 is believed to be due to spin polarized tunneling of electrons between the conventional free layer 18 and the conventional pinned layer 14. Thus, spin polarized electrons tunnel through the conventional barrier layer 16 in order to provide the magnetoresistive effect. When the magnetization of the conventional free layer 18 is parallel or antiparallel to the magnetization of the conventional pinned layer 14, the resistance of the conventional TMR. sensor 10 is minimized or maximized, respectively. In addition, the magnetization of the conventional free layer 18 is biased to be perpendicular to the magnetization of the conventional pinned layer 14 when no external field is applied, as depicted in FIG. 1B. The magnetoresistance, MR, of a MR sensor is the difference between the maximum resistance and the minimum resistance of the MR sensor. The MR ratio of the MR sensor is typically called xcex94R/R, and is typically given as a percent. A typical magnetoresistance of the conventional TMR sensor is approximately twenty percent.
The conventional TMR sensor 10 is of interest for MR sensors for high areal density recording applications. Currently, higher recording densities, for example over 40 gigabits (xe2x80x9cGbxe2x80x9d) per square inch, are desired. When the recording density increases, the size of and magnetic field due to the bits decrease. Consequently, the bits provide a lower signal to a read sensor. In order to maintain a sufficiently high signal within a MR read head, the signal from the read sensor for a given magnetic field is desired to be increased. One mechanism for increasing this signal would be to use an MR sensor having an increased MR ratio. The conventional TMR sensor 10 has an MR of approximately twenty percent, which is higher than a conventional giant magnetoresistance (xe2x80x9cGMRxe2x80x9d) sensor having a nonmagnetic conducting layer separating a free layer and a pinned layer. Furthermore, the conventional TMR sensor 10 has a smaller thickness than a conventional GMR sensor, allowing for a smaller spacing between shields (not shown). The smaller spacing between shields allows for more effective shielding of bits not desired to be read by the TMR sensor 10. The width of the TMR sensor 10, shown in FIG. 1, can be narrower than a conventional GMR sensor. This also aids in allowing the conventional TMR sensor 10 to read smaller bits at higher recording densities.
Although the conventional TMR sensor 10 is of interest for high-density recording applications, one of ordinary skill in the art will readily realize that there are several drawbacks to the conventional TMR sensor 10. Some of these drawbacks are due to the area of the conventional TMR sensor 10. In particular, the conventional TMR sensor 10 often has a nonuniform bias current and may have a reduced MR ratio due to the large area of the TMR sensor 10. The area of the conventional TMR junction includes the area of the interfaces between the conventional pinned layer 14, the conventional free layer 18 and the conventional barrier layer 18. The junction area is defined by the width of the conventional TMR sensor 10, w, depicted in FIG. 1B, and the length of the conventional TMR sensor 10 Into the plane of the page depicted in FIG. 1B. The length of the conventional TMR sensor 10 is determined by the stripe height, h, of the conventional TMR sensor 10 as depicted in FIG. 1A. The width w of the conventional TMR sensor 10 is determined by the track width (not shown) of the media desired to be read and is typically approximately half of the track width. Thus, the junction area for the conventional TMR sensor 10 is the width multiplied by the stripe height (wxc3x97h). The area of the conventional TMR junction for the conventional TMR sensor 10 is typically on the order of one square micrometer. As discussed above, the conventional barrier layer 16 is typically between five and twenty Angstroms thick. Because the conventional barrier layer 16 has such a large area but is so thin, pinholes (not shown in FIG. 1) often exist in the conventional barrier layer 16. Current more easily flows between the conventional pinned layer 14 and the conventional free layer 18 through these pinholes than through the conventional barrier layer 16. As a result, the bias current between the leads 11 and 19 is nonuniform. In addition, because electrons pass readily through these pinholes, the electrons do not undergo spin polarized tunneling. As a result, the MR effect for the conventional TMR sensor 10 can be reduced by the electrons which pass through the pinholes instead of tunneling through the conventional barrier layer 16. Consequently, not only may the bias current lack uniformity, but the MR ratio for the conventional TMR sensor 10 may also be reduced below the intrinsic percentage (approximately twenty percent).
There are further drawbacks to use of the conventional TMR sensor 10. The conventional free layer 18, the conventional barrier layer 16 and the conventional pinned layer 14 are two metallic layers separated by an insulating layer. As a result, the conventional free layer 18, the conventional barrier layer 16 and the conventional pinned layer 14 form a parasitic capacitor. In part because of the large junction area, the parasitic capacitance of the conventional TMR sensor 10 is relatively large. A parasitic capacitance slows the response of the conventional TMR sensor 10. The characteristic time constant for this delay is proportional to the capacitance of the TMR sensor 10. Because the capacitance is larger than desired, the delay is larger than desired. As a result, the response of the conventional TMR sensor 10 is relatively slow and results in a slow data transfer rate.
In addition, the conventional TMR sensor 10 is fabricated and used in the CPP orientation. Typical conventional GMR sensor are fabricated such that a bias current can be driven parallel to the plane of the layers of the conventional GMR sensor. In other words, the conventional GMR sensor is fabricated and used in a current in plane (xe2x80x9cCIPxe2x80x9d) configuration. As a result, it may be difficult to fabricate the conventional TMR sensor 10 using methods developed for the conventional GMR sensor. As a result, the conventional TMR sensor 10 may be relatively difficult to manufacture. Moreover, although the intrinsic MR ratio for the conventional TMR sensor 10 is higher than for a conventional GMR sensor, a higher practical MR ratio is still desired.
Accordingly, what is needed is a system and method for providing a manufacturable TMR junction that is capable of being used in high-density magnetic recording. The present invention addresses such a need.
The present invention provides a method and system for providing a magnetoresistive sensor for reading data from a recording media. The method and system comprise providing a first barrier layer and a second barrier layer and providing a free layer disposed between the first barrier layer and the second barrier layer. The free layer is magnetic. The method and system also comprise providing a first pinned layer and a second pinned layer. The first pinned layer and the second pinned layer are magnetic. The first barrier layer is disposed between the first pinned layer and the free layer. The second barrier layer is disposed between the second pinned layer and the free layer. The method and system also comprise providing a first antiferromagnetic layer and a second antiferromagnetic layer. The first pinned layer is magnetically coupled to the first antiferromagnetic layer. The second pinned layer is magnetically coupled to the second antiferromagnetic layer. The first barrier layer is sufficiently thin to allow tunneling of charge carriers between the first pinned layer and the free layer. The second barrier layer is sufficiently thin to allow tunneling of charge carriers between the second pinned layer and the free layer.
According to the system and method disclosed herein, the present invention provides a magnetoresistive sensor that has a higher magnetoresistive ratio, is relatively simple to fabricate, which is less subject to nonuniform bias current, and which is suitable for high areal density recording applications.